Configuring GitLab Runners

In GitLab CI, Runners run the code defined in .gitlab-ci.yml.
They are isolated (virtual) machines that pick up jobs through the coordinator
API of GitLab CI.

A Runner can be specific to a certain project or serve any project
in GitLab CI. A Runner that serves all projects is called a shared Runner.

Ideally, the GitLab Runner should not be installed on the same machine as GitLab.
Read the requirements documentation
for more information.

Shared, specific and group Runners

After installing the Runner, you can either register it as shared or
specific. You can only register a shared Runner if you have admin access to
the GitLab instance. The main differences between a shared and a specific Runner
are:

Shared Runners are useful for jobs that have similar requirements,
between multiple projects. Rather than having multiple Runners idling for
many projects, you can have a single or a small number of Runners that handle
multiple projects. This makes it easier to maintain and update them.
Shared Runners process jobs using a fair usage queue.
In contrast to specific Runners that use a FIFO queue, this prevents
cases where projects create hundreds of jobs which can lead to eating all
available shared Runners resources.

Specific Runners are useful for jobs that have special requirements or for
projects with a specific demand. If a job has certain requirements, you can set
up the specific Runner with this in mind, while not having to do this for all
Runners. For example, if you want to deploy a certain project, you can set up
a specific Runner to have the right credentials for this. The usage of tags
may be useful in this case. Specific Runners process jobs using a FIFO queue.

Group Runners are useful when you have multiple projects under one group
and would like all projects to have access to a set of Runners. Group Runners
process jobs using a FIFO queue.

A Runner that is specific only runs for the specified project(s). A shared Runner
can run jobs for every project that has enabled the option Allow shared Runners
under Settings > CI/CD.

Projects with high demand of CI activity can also benefit from using specific
Runners. By having dedicated Runners you are guaranteed that the Runner is not
being held up by another project's jobs.

You can set up a specific Runner to be used by multiple projects. The difference
with a shared Runner is that you have to enable each project explicitly for
the Runner to be able to run its jobs.

Specific Runners do not get shared with forked projects automatically.
A fork does copy the CI settings (jobs, allow shared, etc) of the cloned
repository.

Registering a shared Runner

You can only register a shared Runner if you are an admin of the GitLab instance.

Shared Runners are enabled by default as of GitLab 8.2, but can be disabled
with the Disable shared Runners button which is present under each project's
Settings ➔ CI/CD page. Previous versions of GitLab defaulted shared
Runners to disabled.

Making an existing shared Runner specific

If you are an admin on your GitLab instance, you can turn any shared Runner into
a specific one, but not the other way around. Keep in mind that this is a one
way transition.

Go to the Runners in the admin area Overview > Runners (/admin/runners)
and find your Runner

Enable any projects under Restrict projects for this Runner to be used
with the Runner

From now on, the shared Runner will be specific to those projects.

Locking a specific Runner from being enabled for other projects

You can configure a Runner to assign it exclusively to a project. When a
Runner is locked this way, it can no longer be enabled for other projects.
This setting can be enabled the first time you register a Runner and
can be changed afterwards under each Runner's settings.

To lock/unlock a Runner:

Visit your project's Settings > CI/CD

Find the Runner you wish to lock/unlock and make sure it's enabled

Click the pencil button

Check the Lock to current projects option

Click Save changes for the changes to take effect

Assigning a Runner to another project

If you are Maintainer on a project where a specific Runner is assigned to, and the
Runner is not locked only to that project,
you can enable the Runner also on any other project where you have Maintainer permissions.

To enable/disable a Runner in your project:

Visit your project's Settings > CI/CD

Find the Runner you wish to enable/disable

Click Enable for this project or Disable for this project

Note:
Consider that if you don't lock your specific Runner to a specific project, any
user with Maintainer role in you project can assign your Runner to another arbitrary
project without requiring your authorization, so use it with caution.

Manually clearing the Runners cache

How shared Runners pick jobs

Shared Runners abide to a process queue we call fair usage. The fair usage
algorithm tries to assign jobs to shared Runners from projects that have the
lowest number of jobs currently running on shared Runners.

Example 1

We have following jobs in queue:

Job 1 for Project 1

Job 2 for Project 1

Job 3 for Project 1

Job 4 for Project 2

Job 5 for Project 2

Job 6 for Project 3

With the fair usage algorithm jobs are assigned in following order:

Job 1 is chosen first, because it has the lowest job number from projects with no running jobs (i.e. all projects)

Job 4 is next, because 4 is now the lowest job number from projects with no running jobs (Project 1 has a job running)

Job 6 is next, because 6 is now the lowest job number from projects with no running jobs (Projects 1 and 2 have jobs running)

Job 2 is next, because, of projects with the lowest number of jobs running (each has 1), it is the lowest job number

Job 5 is next, because Project 1 now has 2 jobs running, and between Projects 2 and 3, Job 5 is the lowest remaining job number

Lastly we choose Job 3... because it's the only job left

Example 2

We have following jobs in queue:

Job 1 for project 1

Job 2 for project 1

Job 3 for project 1

Job 4 for project 2

Job 5 for project 2

Job 6 for project 3

With the fair usage algorithm jobs are assigned in following order:

Job 1 is chosen first, because it has the lowest job number from projects with no running jobs (i.e. all projects)

We finish job 1

Job 2 is next, because, having finished Job 1, all projects have 0 jobs running again, and 2 is the lowest available job number

Job 4 is next, because with Project 1 running a job, 4 is the lowest number from projects running no jobs (Projects 2 and 3)

We finish job 4

Job 5 is next, because having finished Job 4, Project 2 has no jobs running again

Job 6 is next, because Project 3 is the only project left with no running jobs

Lastly we choose Job 3... because, again, it's the only job left (who says 1 is the loneliest number?)

Using shared Runners effectively

If you are planning to use shared Runners, there are several things you
should keep in mind.

Using tags

You must set up a Runner to be able to run all the different types of jobs
that it may encounter on the projects it's shared over. This would be
problematic for large amounts of projects, if it wasn't for tags.

For instance, at GitLab we have Runners tagged with "rails" if they contain
the appropriate dependencies to run Rails test suites.

Preventing Runners with tags from picking jobs without tags

You can configure a Runner to prevent it from picking
jobs with tags when the Runner does not have tags
assigned. This setting can be enabled the first
time you register a Runner and can be changed afterwards under
each Runner's settings.

To make a Runner pick tagged/untagged jobs:

Visit your project's Settings ➔ CI/CD

Find the Runner you wish and make sure it's enabled

Click the pencil button

Check the Run untagged jobs option

Click Save changes for the changes to take effect

Setting maximum job timeout for a Runner

For each Runner you can specify a maximum job timeout. Such timeout,
if smaller than project defined timeout, will take the precedence. This
feature can be used to prevent Shared Runner from being appropriated
by a project by setting a ridiculous big timeout (e.g. one week).

When not configured, Runner will not override project timeout.

How this feature will work:

Example 1 - Runner timeout bigger than project timeout

You set the maximum job timeout for a Runner to 24 hours

You set the CI/CD Timeout for a project to 2 hours

You start a job

The job, if running longer, will be timeouted after 2 hours

Example 2 - Runner timeout not configured

You remove the maximum job timeout configuration from a Runner

You set the CI/CD Timeout for a project to 2 hours

You start a job

The job, if running longer, will be timeouted after 2 hours

Example 3 - Runner timeout smaller than project timeout

You set the maximum job timeout for a Runner to 30 minutes

You set the CI/CD Timeout for a project to 2 hours

You start a job

The job, if running longer, will be timeouted after 30 minutes

Be careful with sensitive information

With some Runner Executors,
if you can run a job on the Runner, you can get access to any code it runs
and get the token of the Runner. With shared Runners, this means that anyone
that runs jobs on the Runner, can access anyone else's code that runs on the
Runner.

In addition, because you can get access to the Runner token, it is possible
to create a clone of a Runner and submit false jobs, for example.

The above is easily avoided by restricting the usage of shared Runners
on large public GitLab instances, controlling access to your GitLab instance,
and using more secure Runner Executors.

Forks

Whenever a project is forked, it copies the settings of the jobs that relate
to it. This means that if you have shared Runners set up for a project and
someone forks that project, the shared Runners will also serve jobs of this
project.

Attack vectors in Runners

Mentioned briefly earlier, but the following things of Runners can be exploited.
We're always looking for contributions that can mitigate these
Security Considerations.

Resetting the registration token for a Project

If you think that registration token for a Project was revealed, you should
reset them. It's recommended because such token can be used to register another
Runner to the Project. It may be next used to obtain the values of secret
variables or clone the project code, that normally may be unavailable for the
attacker.

To reset the token:

Go to Settings > CI/CD for a specified Project

Expand the General pipelines settings section

Find the Runner token form field and click the Reveal value button

Delete the value and save the form

After the page is refreshed, expand the Runners settings section
and check the registration token - it should be changed

From now on the old token is not valid anymore and will not allow to register
a new Runner to the project. If you are using any tools to provision and
register new Runners, you should now update the token that is used to the
new value.

Determining the IP address of a Runner

It may be useful to know the IP address of a Runner so you can troubleshoot
issues with that Runner. GitLab stores and displays the IP address by viewing
the source of the HTTP requests it makes to GitLab when polling for jobs. The
IP address is always kept up to date so if the Runner IP changes it will be
automatically updated in GitLab.

The IP address for shared Runners and specific Runners can be found in
different places.

Shared Runners

To view the IP address of a shared Runner you must have admin access to
the GitLab instance. To determine this:

Visit Admin area ➔ Overview ➔ Runners

Look for the Runner in the table and you should see a column for "IP Address"

Specific Runners

You can find the IP address of a Runner for a specific project by:

Visit your project's Settings ➔ CI/CD

Find the Runner and click on it's ID which links you to the details page